1. Field of the Invention
The present invention relates to a liquid crystal display.
2. Description of the Related Art
In a liquid crystal display using an optically compensated bend (OCB) mode, a liquid crystal material is caused to form a bend configuration, and the tilt angles of liquid crystal molecules are changed near each alignment layer, thereby changing the optical retardation of an optical filter layer. Because of utilizing the bend configuration, the OCB-mode is one of the display modes capable of realizing a high response speed and a wide viewing angle, and has attracted attention in recent years.
As described above, the bend configuration is essential in the OCB-mode. However, the bend configuration is difficult to stably obtain as will be explained below.
That is, a liquid crystal material of an OCB-mode liquid crystal display forms a splay configuration in an initial state in which the power supply is off. This is because the splay configuration is more stable than the bend configuration by nature. Therefore, a process for changing the splay configuration to the bend configuration is necessary when turning on the display.
In order to induce the transition, it is necessary to supply the liquid crystal material with energy higher than the difference in energies between the bend configuration and the splay configuration. Normally, the energy is supplied to the liquid crystal material by applying voltage to the liquid crystal cell. When the energy is almost equal to the difference of energies, the transition from the splay configuration to the bend configuration will proceed slowly. For this reason, the transition requires that a significantly high voltage be applied. Further, the transition process is prone to be affected by the shape of the substrate surface or the electric field distribution. Consequently, unchanged regions sometimes remain in the optical filter layer.
In order to solve this problem, JP-A 2001-83552 (KOKAI) describes that the pixel electrodes and/or the wirings are patterned into complex shapes so as to produce a non-uniform electric field. JP-A 2006-154797 (KOKAI) describes that the end faces of the pixel electrodes are inclined so as to produce a non-uniform electric field.
When such a technique is employed, under ordinary temperature conditions, the splay configuration can be rapidly changed to the bend configuration with an application of a relatively low voltage. However, the present inventors have found that the transition may not proceed in some regions of the optical filter layer at low temperatures near the lower limit of the temperature range within which the performance is guaranteed.